1. Field of the Invention
The present invention relates to a conjugated diene base rubber composition giving rise to an improved vulcanizate.
2. Related Art Statement
With the recent requirements for the safety and low fuel consumption in the automobiles, there have been demanded excellent conjugated diene based polymers meeting both the above requirements as a rubber material for the tires, particularly a rubber material for the tire treads and so on.
Conventionally, as described in Japanese Patent Publication No. 4,996/69, U.S. Pat. No. 3,956,232, Japanese Patent Application Laid-open No. 205,414/82 and so on, these conjugated diene based polymers have been obtained by polymerizing conjugated diene compound or copolymerizing a conjugated diene compound and a vinyl aromatic compound in a hydrocarbon solvent with use of an organic lithium initiator, and then reacting the resulting product with a halogenated tin compound or an alkenyl tin compound.
However, since the above polymer has carbon-tin bonds in terminals thereof, the carbon-tin bonds are readily cut through a chemical reaction with an acidic substance such as an inorganic acid, an organic carboxylic acid and a Lewis acid, an organic phosphrous compound, and further an organic sulfur compound, or through hydrolysis reaction under a strong acid or a strong alkali to damage the physical properties, and thus additives usable for the rubber composition are restricted.
In order to solve these problems possessed by the prior art techniques, the present inventors have proposed that the branched conjugated diene base polymer excellent in processability, tensile strength, and impact resilience can be obtained by the introducing tertiary amino groups into terminals of the conjugated diene based polymer and further combining a coupling agent such as a tin compound therewith (Japanese Patent Application Laid-open No. 38,209/84), the amino compound used in this technique is insufficient in effects of improving the rolling friction resistance and the wet skid performance of the valcanizate thereof.
Further, natural rubber and a synthetic polyisoprene rubber may be recited as a rubber material excellent in the breaking strength. They are now widely used mainly in the tire treads of the trucks and buses which serve under high load conditions. As compared with the lithium type butadiene polymer (or copolymer) as mentioned above, the natural rubber and the synthetic polyisoprene rubber are inferior in the impact resilience and therefore have been strongly desired to be improved.